The invention relates to an axial piston compressor used in the automobile industry to generate compressed air for a variety of accessories employed in a motor vehicle. Particularly, the invention relates to a variable displacement swash-plate air compressor installed on a vehicle and having pistons the motion of which is predicated on displacement of a swash plate.
A swash-plate axial piston compressor is disclosed on U.S. Pat. No. 5,626,463 to Kimura et al. Typically used as air-conditioning compressors, this type of compressor is known for its complicated mechanical construction which includes at least one movable piston in a cylinder block. The piston conveys the air to be compressed from an intake region into a compression region. The reciprocating action of the piston is effected by a swash plate, which is rotatably mounted on a rotating shaft.
The swash plates acts in conjunction with a take-up plate linked to at least one piston, the plate being positioned in the compressor housing such that it cannot rotate and is supported on a non-rotatable thrust bearing. The purpose of the thrust bearing is to take up the torque that is transmitted from the rotating swash plate to the take-up plate. Compressors of this type are of complex construction in the regions of swash and take-up plates, involving a large number of parts. Furthermore, the discussed compressors require a relatively large space.
Another construction of the swash-plate axial piston type compressor includes a rotatable cylinder block and a stationary swash plate and is disclosed for example in U.S. Pat. No. 5,384,698 to Takagi et al. This structure is also structurally complex and in addition tends to permit oil leakage into the air stream.
It is, therefore, desirable to provide a variable displacement swash-plate air compressor with stationary bores receiving pistons. Also, it is desirable to provide an axial piston compressor wherein an assembly for displacing a swash plate is compact and structurally simple. Furthermore, a variable swash-plate air compressor having pistons the reciprocal motion of which is predicated on displacement of a swash plate is also desirable.
In accordance with the invention, a swash plate of an axial piston compressor moves between a neutral position, wherein forces from the air pressure inside the cylinders and a movable cam acting in opposite directions upon the plate are counterbalanced to cease compression of compressed air, and a second pressurizing position, with the preloading selected at a level below which the air pressure needs to be increased.
Accordingly, the inventive axial piston compressor has a displaceable actuator, which exerts a thrust upon a swash plate to displace pistons in stationary bores of the cylinders. The compressor ceases air-compression when a thrust exerted by an actuator upon the swash plate counterbalances a force generated by pistons upon the swash plate. Thus, the compressor experiences a state of pressure equilibrium, wherein the swash plate lies in a plane extending perpendicular to a shaft supporting the swash plate, and the pistons are idle. The force generated by the pistons is a result of air pressure above the pistons in the stationary cylinder block which is in flow communication with an air system of a motor vehicle, including, but not limited to, a heavy-duty truck.
The compressor is in a working state characterized by reciprocal motion of the pistons after the actuator controllably moves towards and pivots the swash plate in response to a pressure drop in the cylinder block below the thrust generated by the actuator in the state of equilibrium.
In accordance with one aspect of the invention, the actuator includes a plurality of resilient elements attached to a cam element which is in contact with the swash plate. The resilient elements are able to expand at a distance toward the swash plate in response to a pressure drop in the air system of the vehicle which causes the pressure in the space above the pistons to decrease below the thrust generated by the resilient elements. Pistons"" strokes are controlled by an angle at which the swash plate deflects from its vertical or neutral position by a thrust generated by the cam, which is displaced by the expanded washers as the pressure in the air system drops to or below a reference value that is equal to a force generated by the washers in the neutral state of the plate. The swash plate will shift back to the neutral position, wherein the pistons are neutralized, thus discontinuing air production upon reaching the state of equilibrium between the force generated by the washers and the pressure above the pistons.
In accordance with another aspect of the invention, the angle at which the swash plate deflects from its neutral positions is controlled by a servo piston, which may be mounted in a rotating member of a drive shaft. The servo piston is attached to a link coupled to a cam element which is displaced toward the plate at distance corresponding a signal actuating the servo piston and corresponding to a pressure drop in the air system of the vehicle.
It is, therefore, an object of the invention to provide an axial piston compressor having a swash plate controlling the movement of the pistons, which are received in stationary cylinder bores.
Yet another object of the invention is to provide an axial piston compressor wherein the angular displacement of the swash plate is controlled in response to displacement of an actuator after the pressure in an air system of the truck has fall down to or below a reference value.
Still a further object of the invention is to provide an axial piston compressor having a resilient actuator which is controllably displaced relative to the swash plate in order to exert a thrust upon the plate in response to the pressure change in the air system.
A further object of the invention is to provide an axial piston compressor wherein air production is initiated upon disturbing a state of equilibrium, wherein a force exerted by a controllably displaceable cam element upon a swash plate is counterbalanced by a pre-set pressure in the air system of the truck.